Abstract
Salmonella is responsible for a wide range of infections and is a constant threat to public health, particularly in light of emerging antibiotic resistance. The use of bacteriophages and phage endolysins as specific antibacterial agents is a promising strategy to control this bacterial infection. Endolysins are important proteins during the process of bacteria lysis by bacteriophages. In this study, we identify a novel endolysin, named LysSE24. LysSE24 was predicted to possess N-acetylmuramidases activity, with a molecular mass of ca. 17.4 kDa and pI 9.44. His-tagged LysSE24 was heterologously expressed and purified by Ni-NTA chromatography. LysSE24 exhibited optimal bactericidal activity against Salmonella Enteritidis ATCC 13076 at a concentration of 0.1 μM. Salmonella population (measured by OD600 nm) decreased significantly (p < 0.05) after 10 min of incubation in combination with the outer membrane permeabilizer in vitro. It also showed antibacterial activity against a panel of 23 tested multidrug-resistant Salmonella strains. Bactericidal activity of LysSE24 was evaluated in terms of pH, temperature, and ionic strength. It was very stable with different pH (4.0 to 10.0) at different temperatures (20 to 60 °C). Both K+ and Na+ at concentrations between 0.1 to 100 mM showed no effects on its bactericidal activity, while a high concentration of Ca2+ and Mg2+ showed efficacy. Transmission electron microscopy revealed that exposure to 0.1 μM LysSE24 for up to 5 min caused a remarkable modification of the cell shape of Salmonella Enteritidis ATCC 13076. These results indicate that recombinant LysSE24 represents a promising antimicrobial activity against Salmonella, especially several multidrug-resistant Salmonella strains. Further studies can be developed to improve its bactericidal activity without the need for pretreatment with outer membrane-destabilizing agents by synthetic biology methods.
Highlights
Salmonella bacteria is the etiologic agent of salmonellosis for humans in many countries for at least over 100 years [1]
To investigate the thermal stability of LysSE24, 0.5 μM of each endolysin was incubated at different temperatures (20–90 ◦C) in a water bath for 30 min followed by a cooling step to room temperature
The physicochemical properties of the LysSE24 sequence were analyzed by the ProtParam tool
Summary
Salmonella bacteria is the etiologic agent of salmonellosis for humans in many countries for at least over 100 years [1]. They have been optimized by millions of years of evolution to recognize and effectively kill their target cells [11]. Endolysins can be a novel biocontrol agent to kill target bacteria when it is applied exogenously in the form of recombinant proteins This feature has led to a renewed interest, in light of emerging and spreading resistance of bacteria against classical antibiotics [19]. The study of OM permeabilizers (OMPs) has aroused hope; OMPs and phage endolysins can be used to work together on Gram-negative bacteria, such as Pseudomonas, E. coli, and Salmonella [19] To utilize this advantage of endolysins, further efforts and studies need to be conducted on the development of novel phage-based biocontrol agents against foodborne pathogens. An endolysin LysSE24 from the bacteriophage LPSE1 is purified, and its lysis activity is evaluated
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